The invention relates to heating transmission oil using engine exhaust heat. This system increases the temperature of transmission oil during the first several minutes of operation to achieve a fuel economy benefit. Thereafter, the system prevents the transmission oil from overheating.
Fuel economy improvement has been an important objective of automotive research. It is widely recognized that rapid warm up of engine lubrication oil and transmission fluid improve fuel economy by reducing frictional losses and viscosity-related drag losses. Most techniques for warming engine oil and transmission oil include use of heat exchangers that transfer heat from engine coolant to oil during a warm-up period. While this method is effective, it has potential problems. By transferring heat from the engine coolant to oil, less heat is available to warm the passenger compartment, which causes a noticeable delay to vehicle occupants especially during cold weather. Today's efficient engines produce less engine coolant heat; therefore, less heat is available from that source to heat engine oil and transmission oil.
U.S. Pat. No. 6,151,891 describes a heat exchanger for transferring heat from motor vehicle exhaust to transmission oil for the purpose of preheat the oil. U.S. Pat. No. 4,458,642 discloses a lubricant heating system for an internal combustion engine wherein a lubricant is directed into a heating chamber and heated by exhaust gases flowing in an exhaust pipe.
U.S. Pat. No. 5,724,931 discloses a system for controlling the heating of a temperature control fluid using the engine exhaust manifold. An electronic control unit receives signals from one or more sensors, which are indicative of ambient air temperature and engine oil temperature.
Japanese Patent Document 410318348A discloses an automatic transmission for an automobile wherein transmission oil is heated in a heat exchanger, which transfers heat from exhaust gas to the oil.